Electrically powered wheelchairs are commonly fitted with a tilt mechanism which allows adjustment of the orientation of a seat frame comprising a seat part and a backrest part. Electrically powered wheelchairs may also be provided with a lift mechanism which allows adjustment of the height of the wheelchair seat. The combination of these two mechanisms can provide seat frame adjustment such as anterior tilting, i.e. forward tilting, posterior tilting, i.e. backwards tilting, and/or elevation of the seat frame. A seat occupant or caretaker may thereby set the seat position according to desire or current need of the occupant.
When the seat position is altered by the tilt mechanism and/or the lift mechanism, it may be desirable to be able to simultaneously control the position of the armrest of the wheelchair to provide optimal support for the wheelchair occupant during tilt/lift operation as well as in the resulting seat position. This is for example the case when the seat frame is being set into an anterior tilt position. During this entire motion it is advantageous to be able to maintain the armrest parallel to ground. The wheelchair occupant can then feel safe during the tilt operation because the occupant may confidently lean against the armrest, as the armrest is parallel to the ground. On the other hand, when the seat frame is tilted back, it is generally perceived to be more comfortable and safe if the armrest is perpendicular to the backrest and not parallel to the ground.
In existing electrically powered wheelchair designs the tilt mechanism and the lift mechanism have typically been separated. The linkage that controls the position of the armrest may then be coupled to a fixed point on the lift mechanism, to which fixed point the armrest adjustment relates to. In this manner, the armrest is kept parallel with ground during a tilt operation.
Today, electrically powered wheelchairs with a different design concerning the lift/tilt functionality are entering the market. These wheelchairs have a common mechanism for providing tilt/lift. A linkage of the type utilised in the separated tilt mechanism and lift mechanism design would not provide armrest adjustment functionality which, for example, is parallel to ground during tilt operation.